Field of the Invention
This invention relates to a device for executing operation of breadth narrowing compensating for the expansion of the breadth on both sides of a sheet spring material before taper rolling work on the sheet spring material in order to prevent the breadth expansion to be caused by the taper rolling.
According to conventional methods of manufacturing a sheet spring, since the thickness of the sheet spring is always taken as basis, taper rolling work results in expansion of the breadth. Consequently, these expanded portions have to be adjusted by means of cutting and abrading, grinding and abrading, etc. That is, as is shown in FIG. 1, (a) and (b), a process of pinching of the breadth by means of press or a process of breadth narrowing by means of press is required. Further, problems exist in regard to wear and tear of the press mold, maintenance of dimensions and adjustment of fabrication. At times, there appears such a defect that an accident of interpenetration of scales happens.
Moreover, there are many problematical points such that the rate of effective utilization of material is low, unevenness appears in the sheet thickness or buckling occurs to form such a cross sectional shape as shown in FIG. 2. There is also such a defect that emerges after taper rolling, bending or winding to the sheet breadth direction. Many work units are needed to correct these failures. Furthermore, metallurgical instruments for performing heat treatment to sheet springs after their formation have to be particular with each kind of product. Hence, the expenses increase and there are many issues in respect of such control problems as the improvement and the stabilization of product quality.